Semiconductor device capable of minimizing mutual effects between two different operations therein

ABSTRACT

A device includes a control circuit that triggers a first operation every time a specific signal is supplied thereto, and that triggers a second operation in place of the first operation in response to the first specific signal supplied after the number of the first operation performed has reached a predetermined number.

This application is based upon and claims the benefit of priority fromJapanese Patent application No. 2010-050018, filed on Mar. 8, 2010, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

This invention relates to a device such as a semiconductor device havinga refresh function, and a control method thereof.

A semiconductor device including a volatile memory element is requiredto perform a refresh operation periodically to maintain information heldin the volatile memory element. Such periodical operation may beutilized to trigger another operation.

For example, US2007/0148796A1, or JP2007-123987A (Patent Document 1)discloses a technique in which an impedance adjustment (ZQ calibration)at an external terminal is carried out together with a refresh operationin synchronization with a refresh cycle.

JP2005-292947A (Patent Document 2) discloses a technique in whichvariable delay data from a DLL (Delay-Locked Loop) is updated togetherwith a refresh operation in synchronization with the refresh operation.

SUMMARY

When a refresh operation is performed in a semiconductor device having avolatile memory cell, a sense operation is performed simultaneously by aplurality of banks provided in the semiconductor device. Therefore, theelectrical current consumed by the sense operation occupies a relativelylarge part in the entire current consumption of the semiconductordevice. In addition, the current consumed by operations such as ZQcalibration and updating of DLL delay values also occupies a relativelylarge part in the entire current consumption of the semiconductordevice. These operations requiring high current consumption may generatenoise in the chip (in the semiconductor device), which may result inmutually affecting the operations (of others). When several operationsrequiring high current consumption are performed simultaneously, thenoise generated in the chip is increased. Normally, these operations arenot performed simultaneously in a semiconductor device. However, ifthese operations are performed simultaneously, an error may occur insensing operation of each of the refresh operation, the ZQ calibrationoperation, and the DLL adjustment operation.

The present invention seeks to provide a device capable of minimizingthe mutual effect between two different operations when the start of anoperation is utilized to trigger another operation.

In one embodiment, there is provided a device that includes a controlcircuit triggering a first operation every time a specific signal issupplied thereto, and triggering a second operation in place of thefirst operation in response to the first specific signal supplied afterthe number of the first operation performed has reached a predeterminednumber.

In another embodiment, there is provided a system that includes asemiconductor device including a control circuit triggering a firstoperation every time a specific signal is supplied, and triggering asecond operation in place of the first operation in response to thefirst specific signal supplied after the number of the first operationsperformed has reached a predetermined number, and a controller supplyingthe specific signal to the semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be moreapparent from the following description of certain preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram schematically illustrating a configuration ofa semiconductor device according to a first embodiment of thisinvention;

FIG. 2 is a block diagram illustrating a configuration example of a DLLincluded in the semiconductor device of FIG. 1;

FIG. 3 is a block diagram illustrating a configuration example of a ZQcalibration circuit included in the semiconductor device of FIG. 1;

FIG. 4 is a circuit diagram illustrating a configuration example of arefresh execute signal generator of a control logic included in thesemiconductor device of FIG. 1;

FIG. 5 is a diagram for explaining an operation of the refresh executesignal generator of FIG. 4;

FIG. 6 is a block diagram illustrating a configuration example of anadjustment operation execute signal branching circuit included in asemiconductor device according to a second embodiment of this invention;

FIG. 7A is a circuit diagram illustrating a configuration example of aroute selector included in a semiconductor device according to a thirdembodiment of this invention;

FIG. 7B is a table representing a data set for controlling in the routeselector of FIG. 7B;

FIG. 8 is a schematic diagram illustrating a semiconductor deviceaccording to a fourth embodiment of this invention;

FIG. 9 is a circuit diagram illustrating a configuration example of arefresh execute signal generator provided in each memory device includedin the semiconductor device of FIG. 8;

FIG. 10 is a block diagram illustrating a configuration example of asemiconductor device according to a fifth embodiment of this invention;and

FIG. 11 is a block diagram for explaining a refresh timer.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will be now described herein with reference toillustrative embodiments. Those skilled in the art will recognize thatmany alternative embodiments can be accomplished using the teachings ofthe present invention and that the invention is not limited to theembodiments illustrated for explanatory purposes.

A representative example of a technical idea (concept) for achieving theobject of this invention will be described below. However, it should beunderstood that what is claimed in this application is not limited tothis technical idea, but is defined only by the appended claims.

A semiconductor device according to an aspect of this invention triggersa first operation (e.g., operation of a refresh counter 105) every timea specific signal is supplied thereto from at least one of external andinternal timers via a command decoder 109. Once the number of the firstoperations has reached a predetermined number, the semiconductor devicetriggers a second operation (updating of a DLL 114 or ZQ calibration ofZQ calibration circuit 115) in place of the first operation in responseto the next specific signal supplied thereto. For example, the specificsignal may be a refresh command signal, and the first operation may be arefresh operation. Every time the first operation is performed for 2^(n)times (n is a natural number), the second operation instead of the firstoperation is performed in response to the next specific signal. As such,the first operation is not performed while the second operation isperformed. The second operation may be, for example, a delay valueupdating operation of the DLL (Delay-Locked Loop) or a ZQ calibrationoperation. Taking an example, every time the refresh operation isperformed for 32 times (n=5) in response to the refresh command signal,the DLL delay value updating operation or ZQ calibration instead of therefresh operation is performed in response to the next refresh commandsignal. Assuming that the refresh of 32 word lines (refresh addresses)to be refreshed is completed by the refresh operations corresponding to32 refresh commands, one set of operations on all the refresh addressesis completed by 33 refresh commands according to this invention. The DLLdelay value updating operation or ZQ calibration is performed once byone of the 33 refresh commands. As such, the DLL delay value updating orZQ calibration is performed by the 33^(rd) refresh command. Theseoperations are performed under the control of a control circuit providedin the semiconductor device.

As described above, once the number of first operations performed inresponse to input of a specific signal has reached a predeterminednumber, the semiconductor device performs the second operation insteadof the first operation in response to the next specific signal input.This enables the second operation to be performed periodically and at adifferent timing from the first operation (while the first operation isnot performed). Thus, the mutual effects between the first and secondoperations can be minimized or eliminated.

With reference to the accompanying drawings, preferred exemplaryembodiments of this invention will be described in detail.

FIG. 1 illustrates a configuration example of a semiconductor deviceaccording to a first embodiment of this invention. Although thesemiconductor device illustrated here is a memory device, specifically aDRAM (Dynamic Random Access Memory), this invention is applicable notonly to DRAMs but also other semiconductor devices.

The DRAM of FIG. 1 has a memory cell array 101 formed with a pluralityof banks (here eight banks, bank0 to bank7), a row decoder 102 and asense amplifier 103 corresponding to each of the banks, a column decoder104, a row address buffer and refresh counter 105, a column addressbuffer and burst counter 106, a control logic (control circuit) 107, amode register 108, a command decoder 109, a clock generator 110, a datacontrol circuit 111, a data latch circuit 112, an I/O buffer 113, a DLL114, and a ZQ calibration circuit 115.

The memory cell array 101 has a plurality of memory cells (not shown)arranged in array and connected to word lines (not shown) and bit lines(not shown).

The row decoder 102 decodes a row address output by the row addressbuffer and refresh counter 105 and selectively drives a word line of thememory cell array 101.

The sense amplifier 103 amplifies a potential difference generatedbetween a bit line pair by data read from a memory cell.

The column decoder 104 decodes a column address output from the columnaddress buffer and burst counter 106, and selectively connects a bitline of the memory cell array 101 to the I/O line (not shown).

The row address buffer and refresh counter 105 outputs, to the rowdecoder 102, a row address corresponding to an address signal inputthereto or a count value of the refresh counter incorporated therein,under the control of the control logic 107.

The column address buffer and burst counter 106 outputs, to the columndecoder 104, a column address corresponding to an address signal inputthereto or a count value of the burst counter incorporated therein,under the control of the control logic 107.

The mode register 108 holds a data set defining operations of the DRAM.The data set is set and changed using address signals (including bankaddress signals BA0 to BA2).

The command decoder 109 receives a chip select signal /CS, a row addressstrobe signal /RAS, a column address strobe signal /CAS, and a writeenable signal /WE, decodes a command consisting of a combination ofthese signals, and transmits the decoded command to the control logic107.

The control logic 107 controls the respective units based on a commandfrom the command decoder 109 and a data set established in the moderegister 108.

The clock generator 110 generates or stops generating an internal clockto be used in the DRAM upon receiving complementary external clocks CKand /CK and a clock enable signal CKE.

The data control circuit 111 controls input and output of write data andread data.

The data latch circuit 112 latches the write data and the read dataaccording to data strobe signals DQS and /DQS.

The I/O buffer 113 temporarily holds the write data from data terminalsDQ and the read data to the data terminals DQ. Upon receiving a datamask signal DM during a write operation, the I/O buffer 113 masks inputdata. Further, upon receiving an on-die termination signal ODT, the I/Obuffer 113 turns on or off the terminating resistance of each of thedata terminals DQ, the terminals for the data strobe signals DQSand/DQS, and terminals for termination data strobes TDQS and /TDQS.

The DLL 114 generates a signal in delayed synchronization with theexternal clocks CK and /CK upon receiving these external clocks, andsupplies the generated signal to the I/O buffer 113.

The ZQ calibration circuit 115 utilizes an external resistance connectedto the ZQ terminal to generate a resistance control signal DRZQ foradjusting the output resistance of an output driver and the terminatingresistance of each of the above-mentioned terminals, and outputs theresistance control signal DRZQ to the I/O buffer 113.

A configuration example of the DLL 114 will be described with referenceto FIG. 2.

The DLL 114 of FIG. 2 is configured to adjust the rising edge and thefalling edge of its output signal. Generally, the part of the DLL 114depicted in the upper part of FIG. 2 handles the adjustment of therising edge, and the part of the DLL 114 depicted in the lower parthandles the adjustment of the falling edge.

The DLL 114 of FIG. 2 has an input circuit 201, a delay circuit 202,interpolators 203R and 203F, a synthesizer 204, a replica circuit 205,phase detectors 206R and 206F, and phase adjustment circuits 207R and207F.

The input circuit 201 outputs a single-end clock signal DLCLKA uponreceiving the external clocks CK and /CK.

The delay circuit 202 has a rising edge detecting delay line (not shown)and a falling edge detecting delay line (not shown). The delay lines areeach formed by connecting delay elements in multiple stages. The clocksignal DLCLKA from the input circuit 201 is branched and supplied to thedelay lines. In response to a delay selection signal from the phaseadjustment circuit 207R, the delay circuit 202 outputs an output fromone of the even-number-th delay elements on the rising edge detectingdelay line and an output from the subsequent odd-number-th delayelement, as delay signals OUTRE and OUTRO. Further, in response to adelay selection signal from the phase adjustment circuit 207F, the delaycircuit 202 logically inverts an output from one of the even-number-thdelay elements on the falling edge detecting delay line and an outputfrom the subsequent odd-number-th delay element by means of an inverter,and outputs as delay signals OUTFE and OUTFO. The logic inversion by theinverter is performed in order to facilitate subsequent processes. Thus,the delay signals OUTFE and OUTFO are each output as a signal having arising edge corresponding to the detected falling edge.

The interpolators 203R and 203F respectively delay and synthesize delaysignals from the delay circuit 202 in response to bias signals BIASRE/Oand BIASFE/O from the phase adjustment circuits 207R and 207F.Specifically, the interpolator 203R synthesizes the delay signals OUTREand OUTRO, while the interpolator 203F synthesizes the delay signalsOUTFE and OUTFO. The interpolator 203R synthesizes the delay signalsOUTRE and OUTRO such that the rising timing of its output NR is a timingthat is defined by a bias signal BIASRE/O to be between the risingtiming of the delay signal OUTRE and the rising timing of the delaysignal OUTRO. The interpolator 203F synthesizes the delay signals OUTFEand OUTFO such that the rising timing of its output NF is a timing thatis defined by a bias signal BIASFE/O to be between the rising timing ofthe delay signal OUTFE and the rising timing of the delay signal OUTFO.

The synthesizer 204 generates a DLL output having a rising edge thatrises at the rising timing of the output NR of the interpolator 203R,and a falling edge that falls at the rising timing of the output NF ofthe interpolator 203F. The DLL output from the synthesizer 204 issupplied to an output circuit (OE) 208 included in the I/O buffer 113 aswell as to the replica circuit 205.

The replica circuit 205 is a circuit having a delay equivalent to thedelay of an actual signal route from the output of the DLL output fromthe synthesizer 204 up to the output of data to the DQ terminal. Thereplica circuit 205 not only delays the DLL output but also generates arising clock RCLK and a falling clock FCLK and supplies them to phasedetectors 206R and 206F, respectively. The rising clock RCLK is a signalhaving a rising edge at the same timing as that of the rising edge ofthe DLL output, and the falling clock FCLK is a signal having a risingedge at the same timing as that of the falling edge of the DLL output.

The phase detector 206R detects a phase difference between the risingedge of the rising clock RCLK and the rising edge of the external clockCK and outputs a detection result to the phase adjustment circuit 207R.

The phase detector 206F detects a phase difference between the risingedge of the falling clock FCLK and the rising edge of the external clock/CK, and outputs a detection result to the phase adjustment circuit207F.

The phase adjustment circuit 207R has a controller 209R, a counter 210R,a decoder 211R, and a digital-analog converter 212R.

According to the detection result received from the phase detector 206,the controller 209R outputs, to the counter 210R, a control signalindicating whether the phase of the clock RCLK is to be advanced ordelayed.

The counter 210R counts up or down according to a control signal fromthe controller 209R.

The decoder 211R decodes predetermined high-order bits of the output ofthe counter 210R, and outputs it to the delay circuit 202 as a delayselection signal.

The digital-analog converter 212R converts predetermined low-order bitsof the output of the counter 210R into an analog voltage signal, andoutputs it as a bias signal BIASRE/O to the interpolator 203R.

The phase adjustment circuit 207F is configured in the same manner asthe phase adjustment circuit 207R.

The DLL 114 configured as described above generates a DLL output that isdelayed and synchronized with the external clock. The DLL 114 activatethe counters 210R and 210F (and the phase detectors 206R, 206F and thecontrollers 209R, 209F) to update the count values (delay values) of thecounters 210R and 210F according to the control signal (adjustmentoperation execute signal) from the control logic 107. With the exceptionof this update operation, the count values (delay value) of the counters210R and 210F are fixed (operation of the counters is stopped) toachieve reduction of power consumption.

Next, a configuration example of the ZQ calibration circuit 115 will bedescribed with reference to FIG. 3.

The ZQ calibration circuit 115 of FIG. 3 has pull-up circuits 301 and302, a pull-down circuit 303, counters 304 and 305, comparators 306 and307, and resistors 308 and 309.

The pull-up circuit 302 and the pull-down circuit 303 are formed byreplicating the output circuit of the I/O buffer 113 (to form a replicabuffer). The pull-up circuit 301 is also configured in the same manneras the pull-up circuit 302. The impedances of the pull-up circuits 301and 302 are both controlled by a control signal DRZQP. The impedance ofthe pull-down circuit 303 is controlled by a control signal DRZQN. Thesecontrol signals DRZQP and DRZQN are supplied to the I/O buffer 113 as animpedance control signal DRZQ for controlling the impedance of theoutput circuit of the I/O buffer 113.

The ZQ terminal is grounded via an external resistor R having apredetermined resistance value. The pull-up circuit 301 is connectedbetween a power supply potential VDD (not shown) and the ZQ terminal.When the impedance of the pull-up circuit 301 is equal to the resistancevalue of the external resistor R, the potential of the ZQ terminal isequal to a half of the power supply potential VDD.

The resistors 308 and 309 are connected in series between the powersupply potential VDD and a ground potential GND, and a referencepotential Vref equal to a half of the power supply potential VDD isgenerated at the connection point thereof.

The comparator 306 compares the potential of the ZQ terminal and thereference potential Vref, and outputs a comparison result COMP1.

Upon the control signal ACT1 or SELFEX1 being activated, the counter 304performs count operation according to the comparison result COMP1received from the comparator 306. The counter 304 outputs a controlsignal DRZQP according to the count value, so that the impedances of thepull-up circuits 301 and 302 correspond with the resistance value of theexternal resistor R. The control signal DRZQP is used to control theimpedance of a load side transistor in the output circuit of the I/Obuffer 113, so that the impedance of the load side transistor in theoutput circuit corresponds with the resistance value of the externalresistor R.

The pull-up circuit 302 is connected between the power supply potentialVDD (not shown) and a node A, and the pull-down circuit 303 is connectedbetween the node A and a ground potential GND (not shown). When theimpedance of the pull-up circuit 302 is equal to the resistance value ofthe external resistor R, the impedance of the pull-down circuit 303 isequal to the resistance value of the external resistor R if thepotential of the node A is equal to a half of the power supply potentialVDD.

The comparator 307 compares the potential at the node A with thereference potential Vref and outputs a comparison result COMP2.

Upon the control signal ACT2 or SELFEX2 being activated, the counter 305performs count operation according to the comparison result CMOP2received from the comparator 307. The counter 305 then outputs a controlsignal DRZQN according to the count value, so that the impedance of thepull-down circuit 303 corresponds with the impedance of the pull-upcircuit 302. Since the impedance of the pull-up circuit 302 ispreviously matched with the resistance value of the external resistor R,the impedance of the pull-down circuit 303 is consequently correspondswith the resistance value of the external resistor R. The control signalDRZQN is used to control the impedance of a driver-side transistor inthe output circuit of the I/O buffer 113, so that the impedance of thedriver-side transistor in the output circuit coincides with theresistance value of the external resistor R.

As described above, the ZQ calibration circuit 115 performs ZQcalibration (output impedance adjustment of the output circuit of theI/O buffer 113) as required according to the control signals ACT1 andACT2, or the control signals SELFEX1 and SELFEX2. The controls signalsACT1 and ACT2 are control signals based on a command, whereas thecontrols signals SELFEX1 and SELFEX2 are control signals generated bythe control logic 107 when predetermined conditions are satisfied.

Next, the control logic 107 will be described with reference to FIG. 4.The description here will be made only of the parts directly related tothis invention in the internal configuration of the control logic 107,while the description of the other parts will be omitted. Although thefollowing description will be made of a case in which a refresh (Ref)command signal is used as the specific signal (or a case of a refreshexecute signal generating circuit), the invention is not limited tothis, but other signals may be used as the specific signal. Any signalcan be used as the specific signal as long as it can be repeatedlygenerated, but need not necessarily be generated at constant intervals.

FIG. 4 is a diagram illustrating a configuration example of a refresh(Ref) execute signal generation circuit 400 included in the controllogic 107. This Ref execute signal generation circuit 400 is a circuitoutputting a refresh (Ref) execute signal or adjustment operationexecute signal in response to a refresh (Ref) command signal from thecommand decoder 109. The Ref command signal, the Ref execute signal, andthe adjustment operation execute signal are rectangular pulse signals.The Ref execute signal generation circuit 400 can also be regarded as acircuit for outputting a received specific signal as a Ref executesignal or adjustment operation execute signal.

The Ref execute signal generation circuit 400 has an execute signaloutput unit 401, a counter 402, and a selection indicating unit 403.

Upon receiving input of the Ref command signal, the execute signaloutput unit 401 selectively outputs either one of the Ref execute signaland the adjustment operation execute signal according to the selectionindicating signal from the selection indicating unit 403.

The Ref execute signal is output to a first terminal 404 as a firstexecute signal for triggering a first operation, and the adjustmentoperation execute signal is output to a second terminal 405 differentfrom the first terminal 404 as a second execute signal for triggering asecond operation different from the first operation.

Specifically, the Ref execute signal is supplied through the firstterminal 404 to the components for performing the refresh operation,such as the row address buffer and refresh counter 105, and alsosupplied to the counter 402.

The adjustment operation execute signal is supplied through the secondterminal 405 to one of the DLL 114 and the ZQ calibration circuit 115 asdescribed later.

The counter 402 is formed by connecting one-bit counters (e.g., Dflip-flops) in multiple stages (here, six stages C1˜C6) to count (here,to count down) the number of the output Ref execute signals (the numberof pulses). This counter 402 may be provided by utilizing the refreshcounter (or a part thereof) provided in the row address buffer andrefresh counter 105. In this case, the refresh counter functions as apart of the control circuit.

The count value of the counter 402 is transmitted to the selectionindicating unit 403. It is determined, by the number of digits (numberof bits) of the count value transmitted to the selection indicating unit403, how every inputs of the Ref command signal the adjustment operationexecute signal is output. In FIG. 4, a count value having five bits issupplied to the selection indicating unit 403. Therefore, as describedbelow, one adjustment operation execute signal is output every time 33Ref command signals are input. In other words, while 33 Ref commandsignals are input, 32 Ref execute signals are output and one adjustmentoperation execute signal is output.

The selection indicating unit 403 has a 2-cycle measurement unit 411, aNOR gate 412 and an AND gate 413.

The 2-cycle measurement unit 411 receives the lowest one bit in thecount value of the counter 402 and the Ref command signal, and sets itsoutput A “high” upon receipt of the first Ref command signal that isoutput after the lowest one bit in the count value of the counter 402becomes “1”. The 2-cycle measurement unit 411 sets its output A “low”upon receipt of the first Ref command signal that is output after thelowest one bit in the count value of the counter 402 becomes “0”.

The NOR gate 412 sets its output B “high” once the counter 402 hascounted a predetermined number, or once all the input bits have become“0”. In other words, the NOR gate 412 keeps the output level “low” untilthe counter 402 has counted 32 outputs of the Ref execute signal, andchanges the output level to “high” once the counter 402 has counted 32outputs of the Ref execute signal.

The AND gate 413 outputs “high” as a selection indicating signal whenboth the output A of the 2-cycle measurement unit 411 and the output Bof the NOR gate 412 are “high”, and otherwise outputs “low”.

The execute signal output unit 401 outputs the Ref command signal as aRef execute command signal as long as the selection indicating signalstays “low”. However, when the selection indicating signal is “high”,the execute signal output unit 401 outputs an adjustment operationexecute signal in response to a Ref command signal.

FIG. 5 illustrates a relationship among Ref command signal, countervalue of the counter 402, Ref command signal, adjustment operationexecute signal, output A of the 2-cycle measurement unit 411, and outputB of the NOR gate 412.

As seen from FIG. 5, according to this embodiment, the adjustmentoperation execute signal is output once every time the Ref commandsignal is output 32 times. This means that the adjustment operationexecute signal is output once every 33 cycles at which the Ref commandis input.

The DLL 114 can be activated periodically by supplying the adjustmentoperation execute signal to the DLL 114. In other words, the delay valueof the DLL 114 can be updated periodically. The ZQ calibration (capacityadjustment of the output stage) can be executed periodically bysupplying the adjustment operation execute signal to the ZQ calibrationcircuit 115. However, in order to supply the adjustment operationexecute signal to the ZQ calibration circuit 115, two signals SELFEX1and SELFEX2 having a time difference must be generated from theadjustment operation execute signal.

Thus, this embodiment ensures stable operation even with variation intemperature or voltage, while reducing the power consumption. Moreover,since the DLL 114 and the ZQ calibration circuit 115 are operated onlywhen the refresh operation is not performed. Accordingly, the DLL 114and the ZQ calibration circuit 115 are allowed to operate with highprecision, without being affected by internal noise caused by therefresh operation. The operation of the DLL 114 and ZQ calibrationcircuit 115 is stopped during the refresh operation, whereby error inthe refresh operation itself can be prevented.

Further, according to this first embodiment, the input of the Refcommand signal to the counter 402 is inhibited during the output of theadjustment operation execute signal, whereby the count operation of thecounter 402 is stopped. Accordingly, the counter 402 can be used also asa refresh counter without causing a problem that refresh is performedwith a cell (address) to be refreshed left unrefreshed. Further,although the time required for the refresh is increased according tothis embodiment, the increase is not particularly significant, beingabout 3% (66/64≈1.03).

Next, a second embodiment of this invention will be described.

A semiconductor device according to the second embodiment has, inaddition to the components of the semiconductor device according to thefirst embodiment described above, an adjustment operation execute signalbranching circuit 600 shown in FIG. 6 and included in the refresh (Ref)execute signal generation circuit 400.

The adjustment operation execute signal branching circuit 600 hasone-bit counters (e.g., D flip-flops) 601 and 602 connected to thesecond terminal 405 of the Ref execute signal generation circuit 400 ofFIG. 4, and one-shot pulse generators 603 and 604.

One of the one-bit counters, the counter 601 counts adjustment operationexecute signals from the execute signal output unit 401. The otherone-bit counter 602 counts signals obtained by logically inverting theadjustment operation execute signal from the execute signal output unit401.

According to this configuration, pulse signals are output alternatelyfrom the two one-shot pulse generators 603 and 604 every time anadjustment operation execute signal is output from the execute signaloutput unit 401. The output pulse signals from the one-shot pulsegenerators 603 and 604 are output to a third terminal 605 and a fourthterminal 606, respectively.

A pulse signal output to one of the third terminal 605 and the fourthterminal 606 may be used as a first adjustment operation execute signal,and a pulse signal output to the other terminal may be used as a secondadjustment operation execute signal. The first adjustment operationexecute signal is for example supplied to the DLL 114 as a DLLadjustment operation execute signal, while the second adjustmentoperation execute signal is for example supplied to the ZQ calibrationcircuit 115 as a ZQ calibration execute signal. This enables the DLL 114and the ZQ calibration circuit 115 to operate periodically andalternately. In this case, the adjustment of the DLL 114 is performedonce every 66 cycles. The adjustment of the ZQ calibration is alsoperformed once every 66 cycles. Thus, the adjustment of the DLL 114 andthe adjustment of the ZQ calibration are performed alternately every 33cycles.

A third embodiment of this invention will be described below.

A semiconductor device according to this third embodiment has, as shownin FIG. 7A, a selection switch unit 700 included in the refresh (Ref)execute signal generation circuit 400, in addition to the components ofthe semiconductor device according to the second embodiment.

The selection switch unit 700 provides a path for supplying anadjustment operation execute signal output to the second terminal 405 ofthe Ref execute signal generation circuit 400 to the DLL 114 that is acircuit to be controlled, without passing the adjustment operationexecute signal branching circuit 600, a path for supplying theadjustment operation execute signal to the ZQ calibration circuit 115also without passing the adjustment operation execute signal branchingcircuit 600, and a path for supplying the adjustment operation executesignal to the adjustment operation execute signal branching circuit 600.It can also be considered that the selection switch unit 700 is forsupplying a specific signal to one of a first circuit to be controlled,a second circuit to be controlled, and the adjustment operation executesignal branching circuit.

The selection switch unit 700 is formed of a plurality of, here, four,switches (e.g., transistor switches) 701 to 704. The turning on and offof these switches 701 to 704 is controlled by the control logic 107.“On” indicates electrical conducting state, and “off” indicateselectrical non-conducting state. The control logic 107 controls theswitches 701 to 704 on the basis of a data set for controlling theadjustment operation execute signal stored in a mode register 108 thatis set from the outside of the semiconductor device.

FIG. 7B illustrates the data set for controlling the adjustmentoperation execute signal. When the value in the data set is “1”, theadjustment operation execute signal is periodically supplied to the DLL114 or the ZQ calibration circuit 115.

More specifically, the switch 701 is turned off when the data set “DLL,ZQ” is “0, 0” and is otherwise turned on. The switch 702 is turned offwhen the data set “DLL, ZQ” is “1, 0”, and is otherwise turned off. Theswitch 703 is turned on when the data set “DLL, ZQ” is “0, 1”, and isotherwise turned off. The switch 704 is turned on when the data set“DLL, ZQ” is “1, 1”, and is otherwise turned off.

The configuration described above makes it possible to selectivelyrealize a first state in which the adjustment operation execute signalis not supplied to either the DLL 114 or the ZQ calibration circuit 115,a second state in which the adjustment operation execute signal issupplied to the DLL 114 but not supplied to the ZQ calibration circuit115, a third state in which the adjustment operation execute signal isnot supplied to the DLL 114 but supplied to the ZQ calibration circuit115, and a fourth state in which the adjustment operation execute signalis alternately supplied to the DLL 114 and the ZQ calibration circuit115. The DLL 114 has an OR gate (not shown) which receives a pluralityof signals from output nodes of a plurality of switches (702, 704)respectively corresponding to the second state and the fourth state, andit is controlled by the output of the OR gate whether the DLL 114 isactivated or not. Thus, the DLL 114 is activated if any of the switchesis turned on. The ZQ calibration circuit 115 has an OR gate (not shown)which receives a plurality of signals from output nodes of a pluralityof switches (703, 704) respectively corresponding to the third state andthe fourth state, and it is controlled by the output of the OR gatewhether the ZQ calibration circuit 115 is activated or not. Thus, the ZQcalibration circuit 115 is activated if any of the switches is turnedon. It should be noted that the selection switch unit 700 is capable ofexhibiting the advantages of this invention only if it is provided withthe switch 702 and the switch 703.

The switch 701 can be provided between the NOR gate 412 and the AND gate413 and the switches 702 to 704 can be connected to the second terminal405 so that the refresh operation can be carried out without stoppingthe operation of the counter 402 when the data set “DLL, ZQ” is “0, 0”.

Next, a fourth embodiment of this invention will be described withreference to FIG. 8.

The semiconductor device according to this fourth embodiment is a memorymodule 800 having a plurality of memory devices (DRAMs) according to anyof the first to third embodiments. The memory module 800 has a pluralityof DRAMs 801 and a module board 802 on which the DRAMs 801 are mounted.

The DRAMs 801 are supplied with a common command (CMD). Therefore, theseDRAMs 801 are supposed to concurrently perform a refresh operation oncethey are given a Ref command. However, if the counters (402 in FIG. 4)of the DRAMs 801 have different counter values, a situation may arise inwhich some of the DRAMs perform updating of the DLL delay values and theother DRAMs perform the refresh operation. Since these DRAMs 801 have acommon power supply, the DRAMs may be affected by variation in supplyvoltage caused by operation of other DRAMs. This means that some of theDRAMs may be obliged to update the delay value of the DLL 114 in anunstable condition of the supply voltage caused by the refresh operationof the other DRAMs. In this fourth embodiment, therefore, the counters(402 in FIG. 4) of all the DRAMs 801 are previously reset. Thisresetting can be done, for example, using a MRS (mode register set)command or the like. Specifically, as shown in FIG. 9, a MRS commandsignal is supplied to the reset terminal R of each of the one-bitcounters forming the counter 402. This makes it possible to set the samecount value in the counters of all the DRAMs 801, and to enable all theDRAMs 801 to perform the same operation (any of the refresh operation,DLL delay value updating, and ZQ calibration) in response to a Refcommand.

Next, a fifth embodiment of this invention will be described withreference to FIG. 10.

The fifth embodiment relates to an information processing system havinga memory module having at least one DRAM according to any of the firstto third embodiments.

The information processing system 1000 illustrated in FIG. 10 has a dataprocessor 1001, a memory module 1002, a ROM (Read Only Memory) 1003, astorage device 1004, an I/O (input/output) device 1005, and a system bus1006 for interconnecting these components.

The data processor 1001 may be, but is not limited to, a microprocessor(MPU) or a digital signal processor (DSP).

The storage device 1004 may be a hard disk drive, an optical disk drive,or a flash memory.

The I/O device 1005 may be a display device such as a liquid crystaldisplay, or an input device such as a keyboard or a mouse.

It should be noted that the ROM 1003, the storage device 1004, and theI/O device 1005 are not necessarily essential to the informationprocessing system 1000. One or two or more of these may be connected ornot connected according to an intended use of the information processingsystem.

The data processor 1001 and the memory module 1002 may be connectedthrough a local bus depending on the system configuration. Further, thecomponents may be interconnected by using a plurality of buses.

Although the invention has been described in connection with severalpreferred embodiments thereof, it will be appreciated by those skilledin the art that those embodiments are provided solely for illustratingthe invention, and should not be relied upon to construe the appendedclaims in a limiting sense. The invention is not limited to thoseembodiments, but various changes and modification are possible.

For example, the description of the embodiments above has been made interms of a case in which the Ref signal is used as the specific signal.However, it is also possible to use a refresh clock from a refresh timeras the specific signal. The refresh timer is arranged for example in therow address buffer and refresh counter 105 as shown in FIG. 11, andprovides a refresh clock to the refresh counter during the self-refreshperiod. This configuration enables the semiconductor device toperiodically perform the delay value adjustment of the DLL 114 and theZQ calibration even during the refresh period. As a result, the timerequired before an external command can be input after exit from theself-refresh mode (the number of return latencies from power-down modeto active mode) can be reduced. In this case as well, the refreshcounter can be used as the counter 402 of the Ref execute signalgeneration circuit 400. Then, the refresh timer may be provided in thecontrol logic 107. The refresh timer can be utilized also an internaltimer which serves for another purpose in the semiconductor device.

Furthermore, the 2-cycle measurement unit 411 in the selectionindicating unit 403 may be replaced with a 3-cycle measurement unit. Inthis case, the adjustment operation execute signal branching circuit 600activates the DLL 114 and the ZQ calibration circuit 115 in response tothe refresh (Ref) command signal that is supplied twice after apredetermined number of refresh operations. In other words, theadjustment operation execute signal branching circuit 600 successivelygenerates one DLL adjustment operation command signal and one ZQcalibration command signal in response to the adjustment operationexecute signal successively output twice. It does not matter which ofthe DLL adjustment operation command signal and the ZQ calibrationcommand signal is generated first.

Further, the mode register 108 may be either volatile or nonvolatile.

Furthermore, although the description of the embodiments above has beenmade in terms of an example in which the DLL or the ZQ calibrationcircuit is activated in response to the Ref command for refreshing thevolatile memory cell, the basic technical idea of this invention is notlimited to this, but the invention is also applicable to a nonvolatilememory with memory cells the information holding characteristics ofwhich depend on temperature. When this invention is applied to such anonvolatile memory, another periodical command may be used as thespecific signal in place of the Ref command.

The circuit configurations shown in FIGS. 4, 6 and 7 are illustrativeonly, and any other configuration can be employed as long as it iscapable of achieving the operation for which the circuit is designed.

The basic technical idea of this invention is applicable to varioussemiconductor devices. For example, this invention is applicable tosemiconductor devices in general having a memory function, such as CPU(Central Processing Unit), MCU (Micro Control Unit), DSP (Digital SignalProcessor), ASIC (Application Specific Integrated Circuit), and ASSP(Application Specific Standard Circuit). These semiconductor devices towhich the invention is applied can be productized, for example, as SOC(System On Chip), MCP (Multi Chip Package), and POP (Package OnPackage). This invention is applicable to all these semiconductordevices having any of these product forms or package forms.

Further, the transistors used in this invention can be field effecttransistors (FETs), and various FETs including not only MOS (Metal OxideSemiconductor) FETs but also MIS (Metal-Insulator Semiconductor) and TFT(Thin Film Transistor) FETS can be used. Still further, thesemiconductor device may include a bipolar transistor in a part thereof,or other transistors than FETs may be used.

A variety of combinations and selections of the disclosed elements arepossible within the scope of the invention as defined in the appendedclaims. It should be understood that this invention includes variousmodifications and changes that will occur to those skilled in the art inthe light of the foregoing disclosure and technical ideas.

What is claimed is:
 1. A semiconductor device comprising: a plurality ofexternal terminals configured to be supplied with a plurality of commandinformation; a command decoder coupled to the external terminals andconfigured to output a command signal based on the command information;and a signal generation circuit configured to trigger a first operationin response to each of a plurality of occurrences of the command signal,the signal generation circuit being further configured to trigger asecond operation other than the first operation in response to thecommand signal that occurs subsequently to the plurality of occurrencesof the command signal; wherein the signal generation circuit includes acounter updating a count value thereof each time the command signaloccurs to detect the plurality of occurrences of the command signal. 2.The semiconductor device as claimed in claim 1, wherein the commanddecoder receives a chip select signal, a row address strobe signal, acolumn address strobe signal, and a write enable signal, and decodes acommand consisting of a combination of the chip select signal, the rowaddress strobe signal, the column address strobe signal, and the writeenable signal.
 3. The semiconductor device as claimed in claim 1,further comprising a plurality of memory cells, a refresh counter, and aDLL circuit generating a clock signal; wherein the command signal is arefresh command signal; wherein the first operation is to activate therefresh counter circuit to refresh data stored in the memory cells; andwherein the second operation is to activate the DLL circuit to update adelay value of the DLL circuit.
 4. The semiconductor device as claimedin claim 1, further comprising a plurality of memory cells, a refreshcounter, and a ZQ calibration circuit coupled to an external terminal;wherein the command signal is a refresh command signal; wherein thefirst operation is to activate the refresh counter to refresh datastored in the memory cells; and wherein the second operation is toactive the ZQ calibration circuit to adjust the impedance of theexternal terminal.
 5. The semiconductor device as claimed in claim 1,further comprising a plurality of memory cells, a refresh counter, a DLLcircuit, and a ZQ calibration circuit coupled to an external terminal;wherein the command signal is a refresh command signal; wherein thefirst operation is to activate the refresh counter to refresh datastored in the memory cells; and the second operation is to activate aselected one of the DLL circuit and the ZQ calibration circuit, the DLLcircuit updating, when activated, a delay value of the DLL circuit, andthe ZQ calibration circuit adjusting, when activated, the impedance ofthe external terminal.
 6. The semiconductor device as claimed in claim1, wherein the counter is reset to an initial value by a reset signal.7. The semiconductor device as claimed in claim 6, further comprising amode register supplied with a mode register set signal to storeinformation controlling an operation of the semiconductor device, themode register set signal being used as the reset signal.
 8. Asemiconductor device comprising: a first circuit performing a firstoperation in response to a first control signal supplied thereto; asecond circuit performing a second operation in response to a secondcontrol signal supplied thereto; a signal generation circuit respondingto a plurality of occurrences of a command signal to produce the firstcontrol signal a first plurality of times and thereafter produce thesecond control signal at least once, followed by further producing thefirst control signal a second plurality of times; and a command decoderoutputting the command signal; wherein the signal generation circuitincludes a counter updating a count value thereof each time the commandsignal occurs to detect the plurality of occurrences of the commandsignal.
 9. The semiconductor device as claimed in claim 8, wherein: thefirst circuit is a refresh counter that is activated in response to thefirst control signal to refresh data stored in memory cells; the secondcircuit is a DLL circuit that is activated in response to the secondcontrol signal to update a delay value thereof; and the command signalis a refresh command signal that instructs the semiconductor device torefresh the memory cells.
 10. The semiconductor device as claimed inclaim 9, wherein the signal generation circuit further produces thesecond control signal at least once after producing the first controlsignal the second plurality of times.
 11. The semiconductor device asclaimed in claim 8, wherein: the first circuit is a refresh counter thatis activated in response to the first control signal to refresh datastored in memory cells; the second circuit is a ZQ calibration circuitthat is activated in response to the second control signal to adjust theimpedance of an external terminal; and the command signal is a refreshcommand signal that instructs the semiconductor device to refresh thememory cells.
 12. The semiconductor device as claimed in claim 11,wherein the signal generation circuit further produces the secondcontrol signal at least once after producing the first control signalthe second plurality of times.
 13. The semiconductor device as claimedin claim 8, wherein the semiconductor device further comprises a thirdcircuit performing a third operation in response to a third controlsignal supplied thereto; and wherein the signal generation circuitfurther produces the third control signal at least once after producingthe first control signal the second plurality of times.
 14. Thesemiconductor device as claimed in claim 13, wherein: the first circuitis a refresh counter that is activated in response to the first controlsignal to refresh data stored in memory cells; the second circuit is aDLL circuit that is activated in response to one of the second and thirdcontrol signals to update a delay value thereof; the third circuit is aZQ calibration circuit that is activated in response to the other of thesecond and third control signals to adjust the impedance of an externalterminal; and the command signal is a refresh command signal thatinstructs the semiconductor device to refresh the memory cells.
 15. Asemiconductor device comprising: an input terminal supplied with acommand signal; a counter updating a count value thereof each time aninput signal is supplied to thereto; a decoder coupled to the counter todecode the count value of the counter, the decoder producing an outputsignal that takes an active level when the count value is in a targetvalue and an inactive level when the count value is out of the targetvalue; a signal output circuit coupled between the input terminal andthe counter and configured to allow the command signal to be supplied tothe counter as the input signal in response to the output signal of thedecoder taking the inactive level, to prevent the command signal frombeing supplied to the counter as the input signal in response to theoutput signal of the decoder taking the active level, and to produce afirst control signal triggering a first operation in response to thecommand signal that is allowed to be supplied to the counter and asecond control signal triggering a second operation in response to thecommand signal that is prevented from being supplied to the counter. 16.The semiconductor device as claimed in claim 15, further comprising ameasurement circuit that makes the signal output circuit allow a newcommand signal, which is supplied next to the command signal that hasbeen prevented from being supplied to the counter, to be supplied to thecounter as the input signal irrespective of the output signal of thecounter taking the active level.
 17. The semiconductor device as claimedin claim 16, wherein the count value of the counter becomes out of thetarget value in response to the new command signal being supplied to thecounter as the input signal so that the output signal is changed fromthe active level to the inactive level.
 18. The semiconductor device asclaimed in claim 17, further comprising: a refresh counter performingthe first operation to refresh data stored in memory cells; and a DLLcircuit performing the second operation to update a delay value thereof.19. The semiconductor device as claimed in claim 17, further comprising:a refresh counter performing the first operation to refresh data storedin memory cells; and a ZQ calibration circuit performing the secondoperation to adjust the impedance of an external terminal.
 20. Thesemiconductor device as claimed in claim 17, wherein the device furthercomprises: a refresh counter performing the first operation to refreshdata stored in memory cells; a DLL circuit; a ZQ calibration circuit;and a selection circuit responding to the second control signal tochange between first and second states, the first state being to selectthe DLL circuit, and the second state being to select the ZQ calibrationcircuit; wherein in response to the first state of the selectioncircuit, the DLL circuit performs the second operation to update a delayvalue thereof; and wherein in response to the second state of theselection circuit, the ZQ calibration circuit performing the secondoperation to adjust the impedance of an external terminal.
 21. Thesemiconductor device as claimed in claim 20, wherein the selectioncircuit changed between the first and second states alternately inresponse to the second control signal.
 22. The semiconductor device asclaimed in claim 17, wherein the counter is reset to an initial value bya reset signal.
 23. The semiconductor device as claimed in claim 22,further comprising a mode register supplied with a mode register setsignal to store information controlling an operation of the device, themode register set signal being used as the reset signal.